The field of this invention is microfluidic devices and, in particular, a device designed for improved sample loading and injection.
Microtechnology has already and continues to revolutionize numerous aspects of performing operations. As part of this revolution, microfluidics offers small compact devices to perform chemical and physical operations with minute volumes. In this manner numerous events may be simultaneously performed within a small area using orders of magnitude less reagent and sample than possible with conventional 96-well plates. One aspect of microfluidics is the use of capillary electrokinesis to move materials in small volumes from one site to another on a solid substrate. Referred to commonly as xcexcTAS or xe2x80x9clab-on-a-chip,xe2x80x9d these devices offer numerous advantages for performing chemical operations. The devices allow for mixing, carrying out chemical reactions, such as the polymerase chain reaction, genetic analysis, screening of physiological activity of drug candidates, and diagnostics, to mention only the more popular applications. The devices permit the use of much smaller amounts of reagents and sample, permit faster reactions, allow for easy transfer from one reaction vessel to another and separation of charged entities for rapid and accurate detection.
Numerous designs have been described in the literature for performing these operations in conjunction with particular protocols. Generally, one has a plurality of intersecting channels, particularly channels which join at an intersection. By applying appropriate voltage gradients, the volume in which the ions of interest reside can be relatively sharply delineated within a small volume, referred to as a plug. This operation is important in separations, when one wishes to have a high concentration of sample components to be detected in a sample plug, with little of the sample preceding or following the plug. There is interest in identifying different designs and protocols for carrying out plug formation followed by separation.
The invention includes, in one aspect, an improvement in a microfluidics device of the type having a supply channel for holding a sample, a drain channel, and a separation channel for containing an electrolyte buffer, where the supply and drain channels intersect said separation channel at a supply port and a drain port, respectively, and the ports define a sample-volume region in the separation channel between the two ports. The device further includes first, second, third, and fourth reservoirs communicating with the supply channel, the drain channel, and upstream and downstream ends of the separation channel, respectively, such that applying an electrokinetic or pneumatic force between the first and second reservoirs is effective to move a sample from the first reservoir through the sample-volume region in the separation channel and into the drain channel, and applying an electrokinetic or pneumatic force between the third and fourth reservoirs is effective to move a sample in the sample-volume region in the separation channel in a downstream direction.
The improvement, which is designed for improved sample handling, and in particular, improved sample loading and injecting, includes one or both of the following channel configurations, it being understood that in referring to sample streams, it may intend stream of solute ions as occurs in electrophoresis, liquid or ions as in electroosmosis, or streams of liquid containing dissolved or suspended species or particles, as in pneumatically driven liquid.
(a) First and second peripheral channels connecting the supply channel to upstream and downstream regions of the separation channel, respectively, on opposite sides of the sample-volume region. The two peripheral channels are dimensioned and configured such that applying an electrokinetic or pneumatic force between the first and second reservoirs is effective to move a sample from the first reservoir through the sample-volume region in the separation channel and into the drain channel, via the supply and drain channels, and to move electrolyte solution contained in the first and second peripheral channels and upstream and downstream regions of the separation channel toward the sample-volume region and into the drain channel, thereby shaping the sample in the sample-volume region during sample loading in a such manner that the leading and trailing edges of the sample plug are less diffuse, i.e., more sharply defined, than in the absence of such shaping flows; and
(b) Second and third peripheral channels connecting the supply channel and the drain channel, respectively, to a downstream region of the separation channel, respectively. The two peripheral channels are dimensioned and configured such that applying an electrokinetic or pneumatic force between the third and fourth reservoirs is effective to move a sample in the sample-volume region in the separation channel in a downstream direction, and to move electrolyte solution contained in the upstream region of the separation channel through the second and third peripheral channels, a combination of flows known as xe2x80x9cpull-backxe2x80x9d, thereby moving any components contained in the sample and drain channels away from the sample-volume region of the separation channel during sample injection, thereby maintaining or enhancing the lateral definition of the sample plug along its direction of motion.
In one general embodiment, the force applied between the reservoirs is an electrokinetic force produced by placing a voltage potential between the reservoirs.
In another general embodiment, the channel network includes both the first and second peripheral channels, for shaping sample in the sample-volume region during sample loading, and the third peripheral channel, for cooperating with the second channel during sample injection, to move sample contained in the sample and drain channels away from the sample-volume region of the of the separation channel. The device may include a fourth peripheral channel connecting the drain channel to an upstream portion of the separation channel.
The sample and drain ports may be axially aligned within the separation channel, whereby the sample-volume region includes the region of the separation channel between the two ports. Alternatively, the sample and drain ports may be axially offset along the separation channel, whereby the sample-volume region includes the region of the separation channel between the two ports, including the ports themselves.
In another embodiment, which includes the above first and second peripheral channels, the device further includes a second pair of peripheral channels, each of which extends from a first region along the sample channel, adjacent the first reservoir, and a second region along the sample channel adjacent the intersection of the sample channel with the separation channel. The second pair of peripheral channels are dimensioned and configured such that applying an electrokinetic or pneumatic force between the first and second reservoirs is effective to move a sample from the first reservoir through the sample channel toward the separation channel, and to move electrolyte solution contained in the second pair of peripheral channels from the first to the second regions in the sample channel, thereby shaping the sample in the sample channel as if is moved into the sample-volume-region of the separation channel.
In another aspect, the invention includes an improved microfluidics system that includes the microfluidics device above, electrodes adapted to contact liquid contained in the device reservoirs, and a control unit for control of the voltage potential difference between the first and second reservoirs, during sample loading, and between the third and fourth and reservoirs, during sample injection.
These and other objects and features of the invention will become more fully apparent when the following detailed description of the invention is read in conjunction with the accompanying drawings.